Using XML in ASP Applications

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Using XML in ASP Applications

• smohr_at_answerthink.com

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How is XML Used in ASP?

• Divorce Data from Presentation
• Platform Neutral Data
• Enable Automated Data Consumers

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Browser Compatibility

• IE5 Default Style Sheet
• Ships with MSXML
• Mozilla is coming (NGLayout engine)

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Configuring IIS for XML

• Set the MIME type .xml -gt text/xml
• Use Response.ContentTypetext/xml

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Parsers

• Dont reinvent the wheel
• Do use a standard model
• W3C Document Object Model
• Simple API for XML
• Component Software

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W3C DOM

• Tree view of an XML document
• Methods for the creation and modification of XML
  documents
• Document, Node, Element, Collections
• Two Levels
• Level I is a Recommendation
• Level II is a draft containing extensions

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SAX

• Ad hoc standard
• Event based parser
• Application must respond to events -- no tree
• Useful for very large documents or when
  interested only in a small subset of a document

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MSXML

• COM component that ships with IE 5
• Implements W3C DOM, preliminary XSL, some
  Microsoft extensions
• Also available in redistributable version
  (requires some DLLs from IE4 or later)

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Other Parsers

• IBM XML4J (Java) and XML4C (C)
• W3C DOM
• SAX
• DataChannel XJParser
• Evolved from Microsoft partnership
• W3C DOM and SAX

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The Agenda Application
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Document Building Strings

• For small amounts of simple XML

• sXML ltAGENDA_QUERYgtltVENUEgt
  Venue.children(Venue.selectedIndex).text
• sXML lt/VENUEgtltTRACKgt Track.children(Track.s
  electedIndex).text
• sXML lt/TRACKgtltDAYgt Day.children(Day.selecte
  dIndex).text
• sXML lt/DAYgtlt/AGENDA_QUERYgt

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Document Building Data Islands

• For repeated tasks from a standard template
• Also used for data binding
• Add the template to the body
• ltXML id"Query"gt
• ltAGENDA_QUERYgt
• ltVENUE/gt
• ltTRACK/gt
• ltDAY/gt
• lt/AGENDA_QUERYgt
• lt/XMLgt

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Data Islands (continued)

• Manipulate through DHTML methods

• var root Query.documentElement
• root.childNodes(0).text Venue.children(Venue.sel
  ectedIndex).text
• root.childNodes(1).text Track.children(Track.sel
  ectedIndex).text
• root.childNodes(2).text Day.children(Day.selecte
  dIndex).text

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The childNodes Collection

• Property of Node
• NodeList object
• Collection of node objects (except attributes)
• Immediate children of the parent
• 0 to length indices

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Sending the Document to the Server

• GET is simple
• Built into MSXML
• Length restrictions
• POST
• Needs extra support from IXMLHTTP
• No length restrictions

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GET MSXML

• Go to a new page
• window.navigate("http//.../AgendaGet.asp?QueryDo
  c" Query.XMLDocument.xml)
• Load a new document into the parser
• parser.load(http//.../AgendaGet.asp?QueryDoc
  Query.XMLDocument.xml)

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POST IXMLHTTP

• var PostObject new ActiveXObject("Microsoft.XMLH
  TTP")
• PostObject.Open("POST", "http//localhost/XMLASP/A
  gendaPost.asp", false)
• PostObject.send(Query.XMLDocument)

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Getting the XML String

• Use the QueryString collection
• sReqString Request.QueryString("QueryDoc")
• parser.loadXML(sReqString)
• Best for cases where you might not always get XML

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Getting the XML DOM

• Request is an XML document
• Uses IStream support in MSXML
• parser.load(Request)

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Walking the Tree

• Standard tree walking
• Depth first (recursion) or breadth first

• function RecurseTree(node)
• for (var i 0 i lt node.childNodes.length
  i)
• RecurseTree(node.childNodes(i))

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Node Features

• Properties
• nodeName, nodeType
• nodeValue, text, xml
• Collections
• childNodes, attributes

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Node Features (continued)

• Methods
• appendChild, insertBefore, removeChild,
  replaceChild
• cloneNode

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Document Building Objects

• XMLDOMDocument
• createElement, createAttribute
• documentElement
• XMLDOMNode
• text
• appendChild, setAttribute

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Returning the Results

• Set the content type
• Use text manipulation or XML DOM to build a reply
• Response.Write(some_xml)

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Building a Reply using the DOM

• cloneNode to quickly generate similar records
• Build a subtree, set the PCDATA, clone it
• Append the results to the parent

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Building a Reply (continued)

• replyDoc.documentElement replyDoc.createElement(
  "AGENDA")
• sessionSubTree replyDoc.createElement("SESSION")
  
• sessionSubTree.appendChild(replyDoc.createElement(
  "TOPIC"))
• . . .
• sessionSubTree.childNodes(0).text "What Forest?
  I Only See (DOM) Trees."
• . . .
• replyDoc.documentElement.appendChild(sessionSubTre
  e.cloneNode(true))

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Visual Presentation

• Decide when it is going to be viewed instead of
  consumed
• Close to client vs. browser neutrality
• HTML -- flexible, but limits utility and reuse of
  the ASP
• CSS -- easy, but browser issues
• XSL -- powerful! Not standard

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Server-generated HTML

• Walk the DOM tree, translate into appropriate
  (D)HTML
• Can also do on client via DHTML
• Limits you to human clients -- separation of data
  and presentation is lost

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CSS

• In IE5, assign an CSS to the document
• lt?xml version"1.0"?gt
• lt?xml-stylesheet type"text/css"
  href"mstalk1.css" ?gt
• ltAGENDAgtltTOPICgt. . .
• CSS
• TOPIC
• COLOR black
• display block
• FONT-FAMILY Verdana
• . . .

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XSL

• W3C Draft for a presentation language
• Transformation
• Reorganize content
• Pattern-matching and query language
• Can specify context and conditions
• Styling
• Like CSS, but expressed in XML

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XSL Example

• lt?xml version"1.0" ?gt
• ltHTML xmlnsxsl"http//www.w3.org/TR/WD-xsl"gt
• ltBODYgt
• ltxslfor-each selectSESSION"gt
• ltDIVgt
• ltDIV STYLE"font-familyVerdana
• font-size14pt alignleft"gt
• ltxslvalue-of selectTOPIC" /gt
• lt/DIVgt
• . . .

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Summary

• ASP and XML are a powerful match
• MSXML meets common ASP requirements
• XML makes a platform neutral interface
• Explicitly separate data from presentation
• Remember automated consumers!

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Further Resources

• XML Applications (Wrox)
• XML Design and Implementation (Wrox)
• MSXML IXMLHTTP reference -- http//msdn.microsof
  t.com/xml/reference/scriptref/XMLDOM_Objects.asp
• ASP XML Tutorials -- http//msdn.microsoft.com/x
  ml/tutorial/default.asp